World’s largest redox flow battery being built in underground salt caverns

Just last week, Tesla announced it was building the world’s largest lithium-ion battery in Australia, but a German energy company looks set to nab the overall title of biggest battery. Ewe Gasspeicher GmbH is building a redox flow battery in underground salt caverns with enough output to supply a day’s worth of power to 75,000 homes.

A redox flow battery stores electrical energy in liquid electrolytes. Inside the electrochemical cell, two liquids – a positive catholyte and a negative anolyte – are separated by a membrane that allows ions to pass through. When the battery is charging from a power source, electrons are added to the anolyte and released from the catholyte, and that process is reversed while discharging. Charged molecules of each electrolyte are pumped from the cell down into storage tanks, where the energy can be stored for several months.

Ewe Gasspeicher’s battery, called brine4power, is based on a system developed by the Friedrich Schiller University in Jena, which uses saltwater electrolytes with recyclable polymers as the active molecules. Those materials, the team says, are far more environmentally friendly than the heavy metal/sulfuric acid mix that other redox flow electrolytes are often made of.